Variably sensitive frequency discriminator



Aug. 19, 1952 M. PETROFF VARIABLY SENSITIVE FREQUENCY 'DISCRIMINATOR Filed March 4, 1948 Patented Aug. 19, 1.952

VAEIAELY SENSITIVE FREQUENCY nisomMiNA'ron n Merlin Petrofl?, Lake Geneva, Wis., assigner to Stewart-Warner Corporation, Chicago, Ill., a

corporation of Virginia.

Application March 4, 1948, Serial No. 13,035

Z- Claims. (Cl. 1250-27) 'I he present invention relates to electronic indicating and recording means, and is particularly directed to apparatus for recording displacements over a wide range, such, for example, as from a few thousandths of an inch to. two inches, and which is particularly suited'for curve drawing instruments.

One of the primary objects of the .present invention is the provision of a new and improved frequency controlled indicating or recording apparatus.

Another object of the present invention is the provision of a new and improved adjustable sensitivity frequency controlled indicating or recording apparatus, A

A further object of the present invention is the provision of a new and improved frequency controlled indicating or recording apparatus including a frequency discriminator comprising balanced adjustable detuned input circuits for adjustmentof the sensitivity ofthe apparatus.

Other objects andA advantages of the present invention will become apparent from they ensuing description of illustrative embodiments of the invention, in the course of whichreference is had to the accompanying drawing, in which:

Fig. 1 is a schematic illustration of one embodiment of the invention;

Fig. 2 is a, fragmentary schematic illustration of a modied portion ofthe embodiment of; Fig. 1; and

Fig. 3 is a View similar to Fig. 2, of another embodiment.

Referring now to the drawing, and first to Fig.

1, the apparatus of the present invention is illustrated as including indicating andrecording means I0, providing either or both a visualindication and a permanent record of displacement, a device I2r havingy a movable element lil displaced in response to a change in condition, dimension, or the like, and anelectronic circuit I6 interconnecting elements I4 and Iiland translating movements ofv element I2 into frequency variations, changing the frequency variations into voltage changes, and transmitting the voltage changes to the indicatingv and recording means.

The indicating and recording means I0 may l be of conventional construction, such, for example, as a standard voltage actuated chart recorder having a movable element I8 movable to different positions in response to the voltage supplied to the recorder. Its movement isrecorded in known manner upona constant Speed tape or chart, thereby to provide a graph of displacement versus time.

'The device I2 having the displaceable element I4, maybe a device such as a penetrometer, or practically any apparatus having an element moved in response to changes in condition, dis- 2 placement, or time, orA it may be a gauge or the like.

The electronic circuit Ilitranslates the movement or positional changent-element I4f into a control voltage suppliedto the indicator and recorder. This is done, according toone ofthe features of the invention, bytranslating movements of element I-4- into frequencyvariations, and then utilizing the frequency changes asr a source of control voltage applied to appara-tus The movable element Ill controls the frequency of an oscillation generator 20 comprising a tube 22 having a plate 24, a control elect-rode 26, and a cathode 28. Thefrequencyrof the oscillator is determinedby-a tuned inputv circuitl comprising capacitor 30lwhich maybeadjustableand a frequency ,controlling inducta-nce comprising coil 32 and an associated=core34 connected to element I4. The core in aybe ofy the powdered iron type. The controllelectrode isconnected to one end of the inductancea-nd.capacitor through the parallel connectedresistor 3B' and capacitor 38. The cathode is connected ,tov theotherfend of the inductance andv capacitor by conductora-40.

The plate circuit of the oscillator-v includesV a tuned circuit with a broadselectivitycharacteristic, comprising adjustable capacitor 42 andcoil 4a, the plate supply voltage being bypassedY by capacitor 46.

The output of the oscillator is supplied to a frequency discriminatorv 504` which, inaccordance with another feature of thefinvention, is of the balanced detector typewith detunedvk input circuits and in which the detuning isfutilizedas a sensitivity control. Theinputcircuits 52 and 54 comprise variablen capacitors 55 and 58 and coils andv 62, respectively, thecoilsbeing-inductively` coupled to -oscillatorcoilt4.` rIf'he-input circuits are tuned above and below'the median frequency of the oscillator. l y

Sensitivity is varied by variationA ofA capacitors 56 and 58, these being simultaneously` variable to vary the peakseparationof'the input circuits and thereby provide the desired sensitiv-ity control.

fThe balanced discriminator includesalso a tube 64, to the platesl 66 and 68 of "which circuits 52 andA 5f?.y are respectively connected., andresistors, 'I0 and, l2 connected in series to the cathodes 'I4 and l5" associated with plates 66 and 68, respectively, and-'to' the junction of which the junction of the input circuits is connected by,y conductor 18. (The cathode heaters are not shown.) Radio frequencyI bypasscapacitors and 82 are connected across resistorsJUandlZ, respectively. l,

Variable .direct Current central; voltage.y pro portional "to, frequency.' variation aumearsH across.

the series connected resistors l0A and' 12, and'it is supplied. .to ,the indicator recorder through conductor 84 and-L` ground connections 86 and 88. The Various circuit elements may have values and be of types indicated below:

34-1 mh.; Q 'ao-11o 44-1 mh.; Q 30-40 so, s2-.5 mh.; Q 11H25 30, 42-200 mmf. (var.) 38-200 mmf. 1s-50o mmf. 56. 58-300 mmf. (var.) so, sz-25o mmf. afa-10,000 ohms 70, 72-25,000 ohms 30, 34-tuned to 400 kc. 42, liii-tuned to 425 kc. 52-tuned to 524 kc. 54-tuned to 375 kc.

The apparatusof the present invention provides an accurate means for automatically drawing a curve of displacement versus time. The displacement can be that of a device such as a penetrometeror devices' measuring compression or extension in various plastic materials with change in load, vtemperaturerhumidity, or other causes resulting in changes of size or length. The apparatuscan also be used as a gauge and in devices such as wheel balancers. In all cases the movement of the core 34 is affected in response to the conditions, etc., which it is desired to indicate or record. y

The linear movement of the core changes the frequency generated by the oscillator 20. This }or over range desired.

frequency change is vtranslated by discriminator 50 into a variable direct current control voltage proportional to the displacement of the core. The control voltage is supplied to the recording andk indicating apparatus I to provide an indicationand record of displacement.

The detunedinput circuits 52 vand 54 provide an arrangement giving satisfactory readings and output control voltage.` Likewise, they enable the sensitivity of the apparatus to be controlled over a considerable range.

The present apparatus can readily be constructed to indicate and record satisfactorily displacements from a few thousandths of an inch total to a total of two inches. If the displacement is approximately one inch, the coil 34 is constructed to have a length of about two inches, or

y twice the total displacement, since a linear frequency change in response to coil displacement takes place only vover about 50% of the coil. The diameter of the coil and core can readily be determined for any particular application.

If it is desiredY to measure other displacements, say of about g1g inch, the coil should be 11g inch long. In this event, the coil should be of the pancake type so that there will be a greater inductance change for a corresponding movement of the core. l

The sensitivity of the electronic circuit can be adjusted for various coils or for a single coil. Thus, with the case of the two inch coil for use with displacement of about an inch, the sensitivity of the circuit vis .variable 'to such an extent that with this one coil it is possible to draw curves of any total displacement within the range of l/; inch to one inch. It is accordingly possible to use the same circuit with about six interchangeable coil and core combinations to obtain indicationsand graphs of displacements within the range of .002 inchto two inches. A considerable maximum voltage change, for example, in the region of about 60 volts, is obtainable. Y

The embodiment of the invention illustrated in Fig. 2 is quite similar to that of Fig.A 1. The. mainv differences arethe use of two tubes Y90 .and-

92 and a different type of sensitivity control. In this embodiment, the sensitivity is adjustable by simultaneously operable switches 93 adapted to include in the tuned input circuits selected ones of a plurality of capacitors 94A, 94B, 96A, and 96B. l With the selector switch set to include capacitors 94A and 96A in circuit, the apparatus Y has a low sensitivity because of the higher capacity of the capacitors. Capacitors 94B and 96B are of lower'capacity so that when they are in circuit the apparatus hasa higher sensitivity.

file of this patent:

Where greater sensitivity is required, quartz lters 98 and |00 can be used in the input circuits, as illustrated in.-Fig. 3. The lter 98 is selected so as to resonate at a frequency slightly above the median frequency of the oscillator and filter 100 .is selected to resonate slightly below the median frequency.

While the invention has been described in conn nection withV details of certain illustrative em bodiments, it should be understood that these details are not intended to be limitative of the invention except in so far as set forth in the .accompanying claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. For use in a variable frequency measuring apparatus, frequency discriminator having variable sensitivity, comprising first and second tuned input circuits. including respective first and second tuning means for varying the resonant frequencies of the circuits with respect to a median frequency,V unitary manually operable sensitivity control means connected to the tuning means for 'concurrently varying the respective tuning means to vary their resonant frequencies in opposite directions from the median frequency, first and second rectifiers respectively connected with the input circuits, and output circuit means connecting the outputs of the rectifiers in opposition.

2. For use as a variably sensitive frequency discriminator in a measuring apparatus, the combination of first and second tuned input circuits including respective rst and second variable reactive means for varying the resonant frequencies of the circuits with respect to a medianfrequency, manually operable unitary sensitivity control means mechanically connected to both reactive means to increase the resonant fre-` quency of the first input circuit while decreasing the resonant frequencyv of the second input circuit, and Vice versa, first and secondY rectifiers respectively connected with the input circuits, and `output circuit means connecting the outputs of the rectifiers in opposition. f

MERLIN PETROFF.

,REFERENCES lCrrslo The following references are of record 'in the 'UNITED STATES PATENTS Number Name v Date 2,200,863 Schuck May 14, 1940 2,264,151l Reid Nov. 25, 1941 2,282,910 Thompson May 12, 1942 Y2,334,704 Hilferty Nov. 23, 1943 2,361,625 Hansen oct. 31, 1944 2,357,495l oorneuus oct. 23, 1945 Y2,423,616 Rath Ju1y s, 1947 y2,441,035. 1 Rath v May 4, 1948 

